Copper-iron-chromium alloy



Patented Aug. 21, 1951 UNITED STATES PATENT OFFICE COPPER-IRON-CHROMIUMALLOY Allen W. Hodge,\Columbus, Ohio, assignor, by

mesne assignments, to Battelle Development Corporation, Columbus, Ohio,a corporation of a Delaware 7 Claims.

This invention relates to copper base alloys containing iron and smallamounts of chromium, and its principal object is to provide an alloywhich has exceptionally high strength after cold working combined withgood resistance to corrosion, and which also has good enough electricalconductivity to permit its use in electrical equipment.

It has been found that the addition to copper of substantial amounts ofiron along with small amounts of chromium produces copper base, ternaryalloys which can be processed to have particularly good tensile strengthand corrosion resistance. In the production of this alloy, pure copperis desirable but ordinary commercially pure copper is satisfactory. Theaddition of from 5 to per cent iron to the copper effects a verynoticeable strengthening of the resulting alloy. More than 30 per centiron, however, lowers the conductivity of the resulting alloy to a pointbeyond that which is normally found usable in electrical equipment, thatis, below per cent I. A. C. S. (International Annealed Copper Standard).Below 5v per cent iron, the tensile strength of the resulting alloydrops ofl rapidly.

The chromium addition to the instant alloy not only increases thecorrosion resistance, but has a strengthening effect out of proportionto the amount of chromium added. Since the effect of the chromium isdependent upon the iron content, all percentages of chromium are statedbased upon the amount of iron present. When chromium is present inamounts equivalent to from 4 per cent to 7 per cent of the iron presentin the alloys, very good corrosion resistance and high tensile strengthare obtained in the resulting alloy. Good tensile strength may beobtained, however, when as little as 2 per cent chromium based on theiron content is employed, but these alloys have only fair resistance tocorrosion. It is undesirable to have more than 7 per cent chromium basedon the iron content present, because these alloys have proven to be verydiflicult or impossible to fabricate.

As in most alloys, there is normally present small amounts of adeoxidizer, such as magnesium, aluminum or silicon. It is to beunderstood that these ingredients are not an essential part of thepresent alloy, but are more in the nature of adventitious elements whichhave no detrimental effect on the alloy.

There are a number of methods of making the copper base alloy containingiron and chromium which comprises the present invention which 2 will bereadily apparent to those skilled in the art. One method which has beenfound to be very satisfactory for producing the instant alloy comprisesmelting the iron (preferably electrolytic scrap or other pure iron) andcopper together in a magnesium oxide crucible, using a slag cover oflime, alumina and silica sand. Magnesium-copper in suificient quantityto deoxidize the melt is added shortly before pouring, and is completelystirred in with an iron rod. Immediately after the addition of thedeoxidizer, chromium is added, either as ferrochrome or as chromiummetal. The melt is poured into an ingot mold provided with a suitablerefractory hot-top at a temperature of approximately 2,750 E: F.Immediately after pouring, the hottop may be covered with an exothermiccompound to help reduce the amount of pipe formed in the ingot.

In order to enable one skilled in the art to more easily practice thispresent invention the following examples are set forth:

Example 1 In accordance with the melting procedure above set forth, 4.2pounds of iron, 0.23 pound of chromium, 10 pounds of copper, and 0.60pound magnesium copper (10% Mg) were melted to produce a heat having ananalysis of 28.4 per cent iron, 0.92% chromium, and 0.24% magnesium withthe balance copper. The ingot produced from this melt was scalped toclean the surface and then heated in a furnace at 1,550 F. for one-halfhour. The ingot was next hot forged to a 4-inch square after which itwas reheated to 1550 F. for one-half hour. The %-inch square was thenfurther reduced by hot rolling to a /32 in. square in six passes andreheated to 1550 F. for one hour, followed by a water quench. Thesurface of the resulting square was cleaned by sand blasting and furtherreduced by cold rolling to 0.170 in. square in 7 passes. After againheating to 1550 F. for one hour in a natural gas atmosphere and waterquenching the piece, the surface was then sand blasted and pickled in aconventional pickling bath. Employing conventional means for an nealing,quenching and cold drawing the metal, the piecewas then cold drawnthrough dies to produce wires sized to 27 gage, 28 gage and a 29 gage.These Wires were tested and results of these tests are shown in thefollowing table wherein the tensile strength is set forth in p. s. i.and the conductivity in per cent of that of pure copper (internationalAnnealed Copper Standard) The electrical conductivity is improved byaging the alloy for about 1 hour at 1050 F. and cooling slowly to roomtemperature. The wires in the example given were aged during drawing.

Example 2 The electrical conductivity may be further improved somewhatby a step-wise aging treatment, although at a cost of some loss intensile strength. For example, 10-gage wire produced as in Example 1 wasannealed for 1 hour at 1830 F.. quenched and aged 1 hour at 1200 F. Thiswire was drawn to IB-gage and again aged for 1 hour at 1020 F. and 2hours at 840 F. This wire was drawn to 24-gage and aged 2 hours at 750F., after which it was drawn to 2'7-gage and given a stress relievingtreatment of A -hour at 570 F, After this treatment, the wire had thefollowing A charge containing 1.46 pounds of iron, 0.13 pound offerrochrome, 12.84 pounds of copper, and 0.60 pound of magnesium copperwas melted in accordance with the procedure above described. This heathad an analysis of 11.8% iron, 0.17% chromium, 0.28% magnesium, 0.01%silicon, and the balance copper. The ingot thus produced was treated inaccordance with the procedure set forth in Example 1 and-wires having adiameter of 27 gage, 28 gage, and 29 gage were produced as above setforth. Tensile strength tests and conductivity tests were made uponthese wires and the following table sets forth the data therebyobtained.

Tensile Diameter, in. Strength, ,2 3 1 s l. '1 mos .0l30 (27 gage). 141,000 50. 2 .0117 (28 gage) 158, 000 39. .0106 (29 gage) 1 159. 000 48. 4

It is apparent from the above table that less than 2% chromium based oniron content has only a minor effect upon the tensile strength andconductivity of the resulting alloys.

Example 4 period of several weeks, after which it still re tained itsluster. A specimen of copper-iron alloy without chromium turnedcompletely black in this time after similar exposure. Likewise a samplewas placed outside in the atmosphere, accompanied by several commercialbronze and brass specimens. Although this specimen finally tarnished, itremained bright much longer than the other specimens, and did nottarnish as heavily at any time.

Proper processing of the alloy comprising the present invention resultsin a metal having approximately 400% of the tensile strength and about35 per cent of the electrical conductivity of pure copper. Such acombination of mechanical strength and electrical conductivity can haveimportant application in the electrical industry. The corrosionresistance of the copper-ironchromium alloy exceeds that of pure copperwhen the amount of chromium is between four and seven per cent of theweight of iron in the alloy. As previously pointed out, three per centchrornium based on the iron content produces an alloy having a goodtensile strength but low corrosion resistance.

It is apparent from the above-detailed description of the presentinvention, that the present alloy is advantageous in that it produces analloy which combines exceptionally high tensile strength in thecold-worked condition with satisfactory conductivity properties. Thisalloy is furthermore of value in that it is highly resistant tocorrosion. Because of this unique combination of properties, the instantalloy is remarkably suited for electrical contacts or other electricaluses wherein high resistance to corrosion and high tensile strength mustbe combined with good electrical conductivity. The instant alloy is, ofcourse, adaptable to many uses other than electrical, such as springs,hinges, door knobs, and many other uses wherein it could replace bronze.

What is claimed is:

1. A copper-base alloy consisting of from 5 to 30% iron, chromium in anamount equivalent to 3 to 7% of the iron present, and the balancecopper.

2. A copper-base alloy consisting of 28.4% iron, 0.92% chromium, and thebalance copper.

3. A copper-base alloy consisting of from 5 to 30% iron, chromium in anamount equivalent to 4 to 7% of the iron present, and the balancecopper.

4. A- heat-treated and worked, corrosionresistant, copper-base alloycomprising essentially from 5 to 30% iron, chromium in an amountequivalent to from 3 to 7% of the iron present, and the balance copper,said alloy having about 400% of the tensile strength and about 35% ofthe electrical conductivity of pure copper.

5. A heat-treated and worked copper-base alloy having a corrosionresistance exceeding that of pure copper and comprising essentially from5 to 30% iron, chromium in an amount equivalent to from 4 to 7% of theiron present, and the balance copper, said alloy having about 400% ofthe tensile strength and about 35% of the electrical conductivity ofpure copper.

6. A heat-treated and cold-worked corrosionresistant, copper-base alloywire consisting of 28.4% iron, 0.92% chromium, 0.24% magnesium asdeoxidizer, and the balance copper, and having an I. A. C. S. electricalconductivity not less than about 35% of that of copper, and a tensilestrength of at least about 189,000 p. s. i.

ductivity not less than about 39% of that of 5 copper and a tensilestrength of at least 141,000 p. s. i.

ALLEN W. HODGE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Hensel et a1. June 27, 1939 SchwarzkopfOct. 15, 1940 FOREIGN PATENTS Country Date Great Britain May 12, 1927France Mar. 31, 1927 France Feb. 11, 1931

1. A COPPER-BASE ALLOY CONSISTING OF FROM 5 TO 30% IRON, CHROMIUM IN ANAMOUNT EQUIVALENT TO 3 TO 7% OF THE IRON PRESENT, AND THE BALANCECOPPER.